My babbling friend M is on the phone. She's now spent five minutes talking about her niece, twenty minutes talking about her brother (and more importantly how her father and stepmother are raising him), and her volume continues to go up. At the end of this call she's going to be yelling and I'm going to be face-down over the desk bleeding from the ears and with a boredom-induced fork in my eye.

I think you should put the phone down. If she notices, tell her (a) you didn't think she needed a conversational partner, since she was prepared to do all the talking, or (b) you had to go have someone look at your ears because of the bleeding, or (c) that she's boring you to tears and needs to Get a Life.